1. Field of the Invention
The present invention relates to a planar light source unit used in a liquid crystal display device, for example, and to a liquid crystal display device using the planar light source unit.
2. Description of the Related Art
In recently years, as display devices for information technology (IT) devices including personal computers, word processors, etc. and for video equipment including television sets, camcorders, car navigation systems, etc., liquid crystal display devices having lightweight, thin-shaped and low-power-consumption properties have been in heavy usage. Major ones of these liquid crystal display devices have a configuration provided with a built-in lighting unit (planar light source unit) for emitting light from behind a liquid crystal panel in order to realize a bright display screen.
The lighting unit is classified into an edge light type lighting unit and a direct light type lighting unit depending on the disposition place of a light source. The edge light type lighting unit is a lighting unit having a system in which a light source is disposed at the edge of an light guide opposed to the liquid crystal display panel. The direct light type lighting unit has a system wherein plural straight tube light sources, such as fluorescence discharge tubes, are disposed at the back surface of a liquid crystal display panel and a diffusion plate is disposed between the liquid crystal display panel and the light sources. Of these systems, the edge light system is advantageous in making the lighting unit thin and suitable for portable electronic devices, for example.
When a planar light source unit of the edge light system is to be incorporated into a liquid crystal display device, for example, it is necessary to dispose a planar light source equipped with the light guide on the side of the back surface of a liquid crystal display panel. In a conventional thin liquid crystal display device of edge light system using a tubular light source or an LED light source, for example, as a structure for retaining an light guide and sheets, the structure for retaining the shape of a planar light source unit through fit-connection (engagement) between a metal frame disposed at the back surface of a reflection sheet and a plastic frame supporting the outer peripheral portion of the light guide has been adopted (refer, for example, to JP-A 2000-294024).
JP-A 2000-294024 reference discloses a liquid crystal display device equipped with a liquid crystal display panel, a metal bezel and a resin frame that retain the liquid crystal display panel, and a planar light source unit and also discloses a fitting structure in which the frame and bezel are joined to each other through engagement of plural projections protruding from the sidewall of the frame in plural openings formed in the sidewall of the bezel. To be specific, in the liquid crystal display device described in JP-A 2000-294024, a structure of forming holes for fitting (openings) in the metal frame (bezel) laid along the side surface of the display device and fitting the projections of the plastic frame in the holes is adopted as the fitting structure.
In the fitting structure between a metal frame and a plastic frame, however, entails a ready disengagement problem due to a difference in finished dimensions of the metal frame and plastic frame, a variation in assemble of the plastic frame or other such disadvantages. When this fit-disconnection problem arises, dimensional stability of the display device will be deteriorated and the display device will have to be assembled while frequently correcting the position of the plastic frame during the assembly process, resulting in increasing the number of working process and making the processes cumbersome and complicated.
The present invention has been proposed in view of the conventional technical problems mentioned above, and the object thereof is to provide a planar light source unit and a liquid crystal display device that can stably be assembled without inducing disengagement between a metal frame and a plastic frame, excel in dimensional stability, avoid an increase in manufacturing cost resulting from increased number of working process and cumbersome and complicated processes and have structures suitable for their small thickness.